This invention relates to apparatuses for non-contact three-dimensional measurement of bodies according to the introductory part of claim 1 and methods for determining a system of coordinates for measuring points on an apparatus for non-contact three-dimensional measuring of bodies according to the introductory part of claim 9.
The triangulation method is one of the most common methods used in range and length measurement and two- or three-dimensional contour detection. A triangulation sensor is used, and the beam from a laser diode is focused through a lens on the workpiece. It produces a bright light spot. When this light spot is viewed at a fixed angle using a position detector or camera, the place where the spot is shown moves within the image as soon as the intersecting point of the laser beam and the workpiece are moved relative to the sensor. This displacement is measured to determine the distance of the workpiece or its surface contour when moving perpendicular to the illuminating laser beam.
DE 43 01 538 A1 (Apparatus and arrangement for non-contact three-dimensional measuring, in particular for measuring plaster casts of teeth) uses a turntable on which the body to be measured is placed, a triangulation sensor and a data processing and control unit connected to it to determine the geometry of rounded parts. Measurement is based on either
local calibration of each measuring head that must take into account in summary the actual position of measuring surfaces in space by coordinate transformation, or
calibration of the entire measuring system using at least one calibrating body where all points in space that are of interest are entered into a joint calibration table. Calibration cannot be avoided.
DE 44 07 518 A1 describes an apparatus and a method for non-contact measurement of three-dimensional objects based on optical triangulation. The triangulation sensor can be moved in one direction (y direction) and pivoted in the x plane across a preset angular position at a fixed point that can be chosen. This involves two independent movements of the triangulation sensor. The object to be measured is located on the turntable. This turntable on the one hand provides rotary movement, on the other hand it can be moved in vertical direction to the movement of the sensor using another driving mechanism. The movements of the triangulation sensor and the turntable determine the coordinates of the measuring spot of the radiation source. Tilting the triangulation sensor allows measuring most dimensions of undercuts, covered points, pocket holes and similar spots of the object. DE 40 37 383 A1 (Method for continuous contactless measurement of outlines and arrangement for carrying out the measuring procedure) uses triangulation to determine the outer contour line of a moving profile. The sensor only detects the distance to the profile and thus its contour. The measuring spot cannot be placed in a system of coordinates.
DE 195 04 126 A1 (Apparatus and method for contactless measurement of three-dimensional objects using optical triangulation), DE 197 27 226 A1 (Set-up of measuring instruments and method for contactless measurement of the three-dimensional spatial shape of a groove in a spectacles frame), and U.S. Pat. No. 5,270,560 (Method and apparatus for measuring workpiece surface topography) record the outlines of workpieces or workpiece parts to be detected step by step. The respective workpiece or workpiece part is only measured relatively.
Coordinate measurement on an object surface is carried out in DE 40 26 942 A1 (Method for contactless measurement of object surfaces) where images are recorded using a camera. This camera is mounted to an index arm of a coordinate gauging device that can be moved in three spatial directions (x and y directions and pivoting). The object to be measured is located on a turntable.
The problem of the invention described in claims 1 and 9 is to provide easy three-dimensional measurement of the geometry of a body and to easily and correctly match triangulation measurement data with the three-dimensional geography of a body.
This problem is solved by the characteristics listed in claims 1 and 9.
The apparatus for non-contact three-dimensional measurement of bodies and the method for determining a system of measuring point coordinates on an apparatus for non-contact three-dimensional measurement of bodies are characterized by particular simplicity and easy implementation. Advantageously, this makes the apparatus and method applicable in production sites for special workpieces. The design is very simple, and the method requires simple and cost-efficient set-up, which ensures a wide range of uses. The basis of the system is an optical triangulation sensor. The beam of a laser diode is focused through a lens on the workpiece. A light spot emerges on the workpiece. This spot is recorded at a fixed angle by a radiation detector. When the workpiece moves relative to the triangulation sensor, the place where the spot is shown also moves within the image. The outline of the workpiece is determined by measuring this displacement.
Before the workpieces are measured, a system of coordinates for three-dimensional matching of the workpiece geometry is determined in a first measurement. A body with known dimensions of its edges or lines is placed on the turntable and measured during one rotation using the triangulation sensor. The body can be placed on the turntable in any position. Instead of said body, lines can be placed onto or into the surface of the turntable.
The triangulation sensor can scan the workpiece by moving the sensor along just one axis and rotating of the workpiece. Controlled triggering of the respective driving mechanisms and use of the system of coordinates results in continuous detection of the workpiece geometry at a high measuring data rate and precision. The apparatus according to the invention is thus characterized by its minimal design. The low number of movements required, i.e. one translatory movement of the triangulation sensor and a rotational movement of the turntable, results in determining the outline of a body with a minimal error of measurement.
Advantageously, the apparatus is particularly suited for measuring rotationally symmetric workpieces. Advantageously, the method can be used to measure rotationally symmetric workpieces. Control and calculation of workpiece geometry is advantageously controlled using a computer.
Preferred embodiments of the invention are described in claims 2 to 8 and 10 to 12.
The surface profile of the workpiece is detected by one perpendicular movement to the illuminating laser beam of the triangulation sensor according to the improvement described in claim 2.
The angle of radiation incidence from the triangulation sensor can be changed using a hinge or ball-and-socket joint according to the improvement described in claim 3. Elevations or recesses in the workpiece surface that might not be found can thus be detected or spotted easier. The coordinate data of the incident radiation can be determined by measuring the angle of the triangulation sensor.
Image distortions on the detector that result in errors of measurement may occur when bodies are measured whose surfaces scatter the radiation from the radiation source by causing multiple reflections. To prevent these errors as much as possible, at least the areas of interest of a body to be measured are covered according to the improvement described in claim 4 with bodies of known thickness whose surfaces are low-scattering with regard to the radiation used. The thickness of these covering bodies is subtracted from the measured value when evaluating the results of measurement so that the original dimension of the body is a corrected measured value.
Favorable variants for determining the system of coordinates for the workpieces according to the improvement described in claim 5 are parallel lines or body edges the distance of which is known. Accordingly designed bodies or bodies comprising such lines are placed on the turntable.
The system of coordinates has to be measured for commissioning and after a change of location only. Thus the bodies for determining the system of coordinates according to the improvement described in claim 6 are required for these measures only.
According to the improvements described in claims 7 and 8, at least two end stops placed at a distance from each other or a magnet incorporated in the turntable are preferred variants of guided workpiece positioning. These positioning aids also largely prevent position changes of the workpieces on the turntable when the turntable is moving. If workpieces are similar in shape, these positioning aids ensure that approximately the same position is retained when changing workpieces. This results in simplified and faster geometry measurement. Thus production monitoring systems can respond faster to any incorrect changes of the manufacturing process.
The illuminating laser beam of the triangulation sensor may be vertically directed towards the turntable surface according to the improvement described in claim 10.
According to the improvement described in claim 11, it is also preferred when determining the system of coordinates for measuring points to use straight or annular lines as parallel lines or body edges.
The system of coordinates has to be measured for commissioning and after a change of location only. Thus the bodies for determining the system of coordinates according to the improvement described in claim 12 are required for these measures only.